Hello everyone,
it seems a non final version of kopano files has found its way into our internal staging environment and was therefore published with the latest WebApp update.
I have just opened a ticket with Univention to replace the 3.0 version of files in the app with the last 2.x version. For the time in between you can download the packages from https://owncloud.kopano.com/s/tiDj5mGUE6saddm and simply downgrade then yourself with dpkg (after extracting the archive).